Embodiments of the present disclosure relate to image processing and, more particularly, to a lens shading correction method using an infrared component of light, and an image signal processing device and an image sensor system employing the method.
In recent years, digital cameras have prevailed increasingly. A digital camera includes a plurality of light pass filters to transmit light having a specific frequency component, and a plurality of photosensitive elements to sense light passing through the light pass filters. Each of the light pass filters may transmit not only a predetermined frequency component of the light but also an infrared component. In addition, the photosensitive elements sense the infrared component of the light.
An infrared component of light affects a captured image. The image affected by the infrared component of the light shows an object in a different manner from when a person sees the object through their eyes. This is because the image affected by the infrared component of the light inaccurately represents a visible-ray component of the light. That is, the image affected by the infrared component of the light has a low quality. In order to overcome this problem, an infrared cut-off filter may be combined with a rear surface of a lens.
When an image is captured by a camera, shading is caused by a lens. The lens shading is a phenomenon in which one or more photosensitive elements, from among the plurality of photosensitive elements, disposed in an edge region do not receive light sufficiently due to an optical characteristic of the lens. That is, the lens shading causes the object to be inaccurately represented in the edge region of the captured image. In order to overcome this problem, lens shading correction may be performed to compensate for signal intensity attenuation with respect to the photosensitive element(s) disposed in the edge region.
Lens shading correction may be performed based on color temperature information or white balance information. Due to an optical characteristic, a cut-off frequency of an infrared cut-off filter varies depending on a distance between a light-transmitting lens region and the center of a lens. Since intensities of infrared components of different light emitted from different light sources are different from each other, the degree of lens shading varies depending on the type of the light source. Accordingly, even when the lens shading correction is performed based on the same color temperature information or the same white balance information, the quality of the final image may vary depending on the type of the light source. That is, it is difficult to perform lens shading correction accurately.